1. Field of the Invention
The present invention relates to a robot apparatus with a wheel mobile mechanism, a method of controlling the robot apparatus, and a computer program and, in particular, to a robot apparatus with a wheel mobile mechanism having non-holonomic constraints that do not allow translational movement in a horizontal direction, such as an opposed-two-wheel type, a method of controlling the robot apparatus, and a computer program.
In more detail, the present invention relates to a robot apparatus with a wheel mobile mechanism having a non-holonomic constraints with respect to an upper body, a method of controlling the robot apparatus, and a computer program. In particular, the present invention relates to a robot apparatus performing a force control in cooperation with the entire body including a wheel mobile mechanism having non-holonomic constraints with an upper body, a method of controlling the robot apparatus, and a computer program.
2. Description of the Related Art
With the onset of a rapidly aging society, a ratio of senior citizens with respect to people who support them is 1:3.3 at present (2005), and is expected to be 1:2.4 in 2015 and then 1:2.1 in 2025. It is an urgent matter to build a society where senior citizens, whose ratio with respect to the composition of population is rapidly increasing as described above, can live with vitality possibly without becoming in need of nursing care and, even if becoming in need of nursing care, they can be prevented as much as possible from becoming in a worsened condition, thereby being able to lead a self-supporting life.
With the onset of such an aging society, in senior nursing facilities and homes with senior citizens, demands for mechatronics devices aiming at mentally and physically assisting the senior citizens are increasing. Also, there are other demands for insertable-type physical supports, such as autonomous-walking assistive devices and power assist for an upper limb, and agent-type physical supports, such as those autonomously moving to carry an object on the floor and do the cleaning.
For example, a robot moves as a leg-mobile type or a wheel type. A leg-mobile robot can support a walking surface with asperities on an operational route, such as a rough terrain or obstacle, and a discontinuous walking surface, such as in ascending or descending stairs or a ladder, thereby performing flexible moving operations. However, the leg-mobile robot has problems, such as the number of joints is increased to incur high cost, the posture is unstable, and walking control is difficult. For example, when the robot topples over, the robot may damage a person with a limp in need of nursing care. By contrast, a wheel-type robot can have a smaller number of joints to suppress cost, the posture is stable, and there is less fear of toppling over.
The mobile mechanism of the wheel type can be broadly divided into an omnidirectional type and a non-holonomic type. “Non-holonomic” means, for example, “the constraint condition of the dynamical system is not integrable”, “a drift is present”, and “coordinates more than the number of inputs can be controlled”. A mobile mechanism of a non-holonomic type is configured with a simple structure, such as opposed two wheels. Although it is difficult for the mobile mechanism to instantaneously advance in a direct horizontal direction (left and right), the mobile mechanism can be manufactured at low cost. For example, the wheel mobile mechanism of an opposed-two-wheel type is adopted in many mobile robots as a practical moving mechanism (for example, refer to Japanese Unexamined Patent Application Publication No. 2007-257200 and Yasuhisa Hirata, Kazuhiro Kosuge, Hajime Asama, Hayato Kaetsu, and Kuniaki Kawabata, “Transportation of a Single Object by Multiple Distributed Robot Helpers with Caster-like Dynamics (DR Helpers) in Cooperation with a Human”, Journal of the Robotics Society of Japan, Vol. 21, No. 7, pp. 776-784, 2003).
When a main use is for physical support described above, mechatronics devices perform operations as flexibly and safely making physical contact with the human and complex environment. That is, unlike the situation in which industrial robots in the past perform fixed operation under a familiar environment, the mechatronics device appropriately adjusts a generation force of an actuator by sensing an unfamiliar environment and obtaining an appropriate external force from the surrounding environment varying with time so as to accomplish a target operation (task). Also, a flexible reaction in consideration of safety is expected against an unfamiliar disturbance that can act on every part of the body.
Most of the robots in the past are of a position control type, giving an angle instruction value to a joint-driving actuator to drive the joint so as to follow the instruction value. A robot of a position control type is easy to control, but has trouble with “soft” control with a force or acceleration order. By contrast, a robot of a force-control type directly controls a joint generation force to directly control force, and therefore can provide more-flexible personal physical interaction services of a force order.
As for leg-type robots, several methods of cooperatively using joints of the whole body including a leg joint with multiple degrees of freedom to perform a force interaction at every place of the entire body have been suggested (for example, refer to L. Sentis et al. “A Whole-body Control Framework for Humanoids Operating in Human Environments” (In Proc. IEEE Int. Conf. on Robotics and Automation, 2006, pp. 2641-2648) and K. Nagasaka et al. “Motion Control of a Virtual Humanoid that can Perform Real Physical Interactions with a Human” (In Proc. 2008 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2008, pp. 2303-2310)).
On the other hand, a whole-body cooperative-force interaction method using a wheel mobile mechanism of an opposed-two-wheel type is not necessarily clear. For example, a wheel-type robot apparatus performing a cooperative control of a force order over a mobile base and arms has been suggested (for example, refer to Khatib, O., Yokoi, K., Chang, K., Ruspini, D., Holmberg, R. Casal, A. “Vehicle/Arm Coordination and Multiple Mobile Manipulator Decentralized Cooperation” (Proc. of IEEE/RSJ Int. Conf. Intelligent Robots and Systems, IROS '96, 1996, pp. 546-553)). However, an omnidirectional mobile body is used as a mobile base, and therefore non-holonomic characteristics are not shown.
To built a whole-body cooperative control system in a robot of an opposed-two-wheel type, kinematical constraints of being not able to make a translational move in a horizontal direction (that is, non-holonomic constraints) are considered, thereby posing a complication even with a simple structure. Also, kinematics of a wheel unit and kinematics of an upper limb have different features, and therefore it is difficult to merge them together. The inventor thinks that these problems make it difficult to achieve a whole-body cooperative-force control in an opposed-two-wheel robot.